I seem to remember that it was shortly after my daughter's third birthday that her father finally put into words what we had both been thinking for a long time. The awful truth about our child. "Have you noticed that she's more right-wing than Enoch Powell?" he sighed.

It was true. A couple of educated, liberal people living at the end of the 20th century had met, mated and produced... well, what had we produced? Evie hated abroad. We loved it. When we took her to a Greek island and were sitting in a taverna swagged with bougainvillea on a warm, heady evening, she uttered her first sentence: "Want go home." And then later, and loudly throughout the holiday: "Want go home." Our Little Englander viewed any subsequent attempts to take her off her native soil with grave suspicion. "Are we in England?" she would ask accusingly as the Eurostar pulled out of Waterloo.

Before becoming parents, I think we assumed that life would go on much as normal, with the added bonus of another curious pair of eyes. Our daughter demurred. Abroad was hot and far away and so foreign. She was happier sitting on Camber Sands in the rain with a plastic bucket and half a dead crab. We liked adventure. She liked routine. (In fact, if you deviated from her routine, all hell would break loose.) We ate on the run. Like an old person, she liked regular hot meals, preferably eaten with her own Teletubbies spoon laid out on her Pooh Bear placemat and drinking from her Piglet beaker. We travelled light. She had more kit than Louis XIV.

Looking back now, I can see how disastrously the two worlds collided. On the one hand, there were the enlightened values I had held dear before parenthood and then along came baby. Baby was a tyrant - she simply didn't do democracy. Attempts to reason with her always ended in tears - usually mine. Raised quite strictly myself, I was determined to bring up my own kids in a different way - there would be discussion instead of diktats, fun not holding your knife properly. Ha! What did I know? Children may behave like liberals - they believe they should be allowed to do what they want - but what they really like, what makes them feel safe, is essentially conservative.

My child was one of Nature's Tories pitted against a mother who was one of nurture's lefties: it was no contest. So you think that if you can keep your daughter out of a pink tutu, she'll have more chance of becoming a brain surgeon? Just try it sometime. Evie was more of a girlie than Julian Clary. The No Barbie rule was flouted: soon there were hundreds of the vile creatures mutating all over the house, legs akimbo and so sensationally slutty it could only be a matter of time before they became a Tracey Emin exhibit. Flamenco Barbie, AC Milan Barbie (I'm not making this up) and a terrifying über-blonde with sightless blue eyes in jodphurs and black boots that Evie's dad christened Klaus Barbie.

One day, in an attempt to stem the toxic tide, I brought home a Scandinavian doll which looked like a Barbie designed by a feminist committee: a wholesome small-breasted individual wearing khaki, she clearly worked at something useful in developing countries. Alas, this poor social democrat never got to meet the Barbies. "It's a boy!" my daughter yelled in horror, before dropping the liberal compromise in the bucket her baby brother reserved for drowning snails.

It was clear that resistance was useless. My bien-pensant ideas fell like Evie's pink skittles. Despite all our best efforts, our girl behaved like a girl, our boy, Thomas, behaved like a boy (snail infatuation, abseiling off sofa) and so, in due course, the parents started to behave like parents. Our laid-back household introduced rules and regulations. We found ourselves using words like structure and bedtime. Justice became summary instead of negotiable and was often unfair. BECAUSE I SAY SO!

And then there were the really painful clashes of ideology. Such as the day my daughter announced that she didn't want me to work. "I want you to stay home," she said. I was ready with all the arguments, of course. Mum and dad both needed to earn money to pay for our house and for all the things she enjoyed doing like violin lessons and going on holiday. Mummy had a job she was good at and it was really important for women to work as well as men. The speech built to a stirring climax - trumpets, choirs, the tearful sisterhood waving flags - in which I assured my daughter that she would understand it all when she was a big girl and wanted to do interesting things herself. Unfortunately, the case for equal opportunities, long established in western society, cuts no ice in the fundamentalist regime of the five-year-old. There is no God but mummy, and daddy is her prophet.

My ideals told me that men and women could both go out to work and be truly equal. My children told me something more complicated, something I really didn't want to hear. Their need for me was like the need for water or light: it had a devastating simplicity to it. It didn't fit any of the theories about what women were supposed to do with their lives, theories written in books often by women who never had children. Children change your heart: they never wrote that in the books. When Evie said, "I wish the weekends were weeks so you could be with us more, Mum," what was the politically correct response to the tears that jumped into my eyes?

It was partly thinking about all this that prompted me to write a novel about the life of a stressed-out working mother. I Don't Know How She Does It tells the story of 35-year-old Kate Reddy. A fund manager in the surreally sexist environment of the City, Kate is a mother of two small kids who, with a husband, Richard, in a failing architecture practice, has ended up as the main breadwinner. One of the things the novel tries to show is how the arrival of two kids can shatter the pre-parental fantasy of closeness. The demands of the children take a terrible toll on a relationship already under acute strain from the mother working so hard. "Any woman with a baby has already committed a kind of adultery," says Reddy.

When I handed the manuscript in, my editor pointed out that the children were the wisest characters in the book. They instinctively know what matters: their poor mother has to find out the hard way.

So much of what my own two babies taught me made it into the novel. When we first brought my daughter home from the hospital six years ago, I remember lowering her in the little seat with the handle on to the hall floor and wondering, so what do we do now? Back then, we were still scared and thought we could break her, not knowing it was more likely to be the other way round.

In fact, needless to say, it's Little Enoch who has changed us. Now we obediently take our holidays at the British seaside. We drive an estate car whose gas-guzzling habits my younger bike-riding self would have scorned. I have adopted a stand on law and order of which Jack Straw would be proud. And we have even started having a Sunday roast with all the trimmings. I still haven't felt tempted to vote for Iain Duncan Smith yet, thank God, but I know that I no longer see the world in red and blue. It's more grey-green - the colour of my daughter's eyes.

· I Don't Know How She Does It: The Life of Kate Reddy, Working Mother is published today by Chatto & Windus. To order your copy for £10.99 plus p&p call Guardian Book Service on 0870 066 7979. Any working mothers who would like to share their stories can contact Kate@KateReddy.com.